One of the central problems associated with long distance Free Space Optics (FSO) is collecting enough signal at the detector to effectively receive data. Even if the correct wavelength of light is selected and the finest optics are used, light (even laser light) will disperse over distance due to a variety of factors including precipitation, temperature differentials, optical element stability, airborne particulates, off angle collection and effective steering. At great distances these factors have an even greater impact leading to dropped or corrupted data. This leads to a higher data error rate which is detrimental to high speed data transmissions. The invention in question when coupled with a Fresnel Lens significantly mitigates signal loss due to off angle collection, steering problems within stated parameters and by orders of magnitude improves the signal focus on the detector. While proper steering of the signal source and collection optics is key, the invention in question allows for relatively large imperfections in steering and still concentrates a great deal of dispersed signal onto the very small detector.
The prior art also includes the following patents and patent applications. U.S. Pat. No. 7,898,665, entitled “Light Emitting Diode Illumination System,” discloses a system to generate a variety of high brightness light sources with varying emission spectra using light emitting diodes. Unlike the present invention, Bruldlacchio et al. discloses a method that incorporates the use of a compound parabolic concentrator (CPC) used to convert light emitted over a hemisphere while preserving the etendue and maximizing the brightness. The prior art also replacing the CPCs with imaging optics to maximize brightness of light emitted within the system. The prior art also discloses the use of a ball lens to reduce the angular extent of the light source, allowing for simpler optical collections into or onto the desired target areas. The present invention does not require such a specific setup, is not concerned with imaging optics and is not concerned or designed to improve localized brightness leaving the optical system in a medical situation like this endoscope. U.S. Pat. No. 7,898,665 is hereby incorporated by reference into the specification of the present invention.
U.S. Pat. No. 6,516,116, entitled “High Speed Optical Receiver,” discloses a system designed to improve high-speed data rates. Unlike the present invention, Murray et al. discloses a receiver that attempts to improve the aperture size of a small detector. Unlike the present invention, Murray et al utilizes a focus lens that has a small f-number (f#) and requires the spot size of that light (DDL) to be significantly smaller than the DCPC in order to put as much light onto the detector. However, the consequence of using a focusing lens with such a small f # is that the focal angle is much larger than the acceptance angle for much of the lens. Consequently, light rays largely pass through the CPC or bounce out through the entrance aperture. Thus only a small portion of the focused light actually hits the detector. In contrast, the present invention improves light collection and pointing by at least a factor of 25. U.S. Pat. No. 6,516,116 is hereby incorporated by reference into the specification of the present invention. Unlike the existing prior art, the present invention funnels significant orders of magnitude more of the signal on the detector, allows for convergent and divergent light sources and ensures stable, high-speed data rates over a wider array of free space optical environments.